Method of coating an article of magnesium and its alloys with mercury



Patented Oct. 12, I954 IVIETHOD F COATING AN ARTICLE OF MAGNESIUM AND ITS ALLOYS WITH MERCURY Paul Klain, Midland, Mich., assignor to The Dow Chemical Company, Midland, Mich, a corporation of Delaware No Drawing. Application February 13, 1952, Serial No. 271,423

2 Claims. 1

The invention relates to a method of amalgamating the surface of an article of magnesium and alloys thereof in which magnesium is the predominant constituent.

It is an object of the invention to secure a firmly adherent layer or coating of mercury on the surface of an article of magnesium and the magnesium base alloys so as to facilitate the soft soldering thereto of other metallic objects.

Other objects and advantages of the invention will become apparent from the following description of the invention.

The invention is predicated upon the discovery that by treating the surface of the object of magnesium or magnesium base alloy to be amalga mated with an alcoholic (ethyl alcohol) nitric acid solution not containing more than 10 per cent of water and bringing a quantity of mercury into contact with the so treated surface in the presence of the solution amalgamation readily takes place. After rinsing and drying the so treated surface soft soldering thereon can be carried out readily in conventional manner.

For the purpose of the invention ordinary commercial concentrated nitric acid may be used preferably containing at least 68 per cent of HNOs, and ethyl alcohol preferably containing not more than per cent of H20, if any. The nitric acid and the ethyl alcohol are mixed in proportions such that the HNOs content of the resulting mixture is between about 1 and 20 per cent by weight, and the water not over about per cent, the balance being ethyl alcohol, C2H5OH. A preferred composition is: HNO3 10 per cent, H2O less than 3 per cent, C2H5OH balance.

A convenient way to carry out the method is to place a quantity of mercury in a vessel and cover it to a depth of 1 to 3 inches with the alcoholic nitric acid composition formulated in the foregoing proportions. The article to be coated or amalgamated with mercury is then slowly passed through the alcoholic nitric acid composition into the mercury. In this way the surface of the article becomes etched clean by the alcoholic nitric acid solution and the so cleaned surface is brought into contact with the mercury before the surface has a chance to become con- 2 taminated. The resulting coated article is withdrawn and rinsed with water and dried preferably in a current of warm air.

In instances where it is impractical to immerse th article to be coated the alcoholic nitric composition may be applied to the surface of the article with a brush and at the same time a quantity of mercury is placed on thesurface so that the mercury is brought into contact with the surface of the article in the presence of the alcoholic nitric acid solution.

The following example is illustrative of an embodiment of the invention.

A magnesium base alloy sheet 0.062 inch thick and having the nominal composition of 3 per cent, Al, 1 per cent Zn, per cent Mn, the balance being magnesium is freed from dirt and grease. The clean sheet is laid horizontally and a drop of mercury is placed upon the sheet followed by a few drops of a mixture of 10 parts by weight of 68 per cent nitric acid and parts by weight of absolute ethyl alcohol over the inercury. The mercury drop flattens, spreads, and becomes alloyed with the surface of the sheet in a matter of seconds. The so treated area is rinsed in water and dried. The mercury-alloyed area of the sheet readily accepts soft solder.

I claim:

1. The method of forming a mercury containing coating on the surface of an article of magnesium and its alloys which comprises bringing together and into contact with the surface Ff the article both liquid mercury and an alcoholic nitric acid solution said solution containing by weight from 1 to 20 per cent of HNO3, less than 10 per cent of H20, the balance being ethyl alcohol.

2. The method according to claim 1 in which the alcoholic nitric acid solution contains about 10 per cent of HNO3, less than 3 per cent of H20, the balance being ethyl alcohol.

References Cited in the file of this patent UNITED STATES PATENTS Number 

1. THE METHOD OF FORMING A MERCURY CONTAINING COATING ON THE SURFACE OF AN ARTICLE OF MAGNESIUM AND ITS ALLOYS WHICH COMPRISES BRINGING TOGETHER AND INTO CONTACT WITH THE SURFACE OF THE ARTICLE BOTH LIQUID MERCURY AND AN ALCOHOLIC NITRIC ACID SOLUTION SAID SOLUTION CONTAINING BY WEIGHT FROM 1 TO 20 PER CENT OF HNO3, LESS THAN 10 PER CENT OF H2O, THE BALANCE BEING ETHYL ALCOHOL. 